An exciting period of exploration of the outer solar system is underway by spacecraft, by remarkably improved ground-based observations and by orbiting telescopes: International Ultraviolet Explorer (IUE) and Hubble Space Telescope (HST). These studies have revolutionized our understanding of the solar system revealing a kaleidoscope of unusual worlds. Because of the low surface temperatures, typically < 130K, ice is the 'rock' in the outer solar system. That is, excluding the four giant planets and Io, it is the structural and thermal properties of ice that determines the surface geology of many objects from the orbit of Jupiter outward (Burns and Matthews, 1986). Therefore, understanding the radiation chemistry of and desorption from ice or low-temperature hydrated minerals is critical. Other more volatile molecular species, such as N2, O2, CO, CO2, NH3, CH4, and SO2 form atmospheres and polar 'ices' or can cause the surface to be geologically active. Io, a moon of Jupiter, is an exception. Owing to its tidal interaction with Jupiter, Io is volcanically active and has lost its water and other light volatiles. Because of this, frozen SO2, a volcanic gas on earth, covers Io's surface (Burns and Matthews, 1986).Since most small, outer solar system bodies, with the exception of Titan, have either no atmospheres or tenuous ones, their icy surfaces are exposed to the solar UV and to the local plasma causing desorption as well as physical and chemical alterations (Johnson, 1990; 1998). During the Voyager I tour of the outer solar system, W.L. Brown, L.J. Lanzerotti and colleagues at AT&T Bell Labs measured the ejection of molecules induced by energetic ion impact of ice. They discovered that the sputtering from low-temperature ices by fast, light ions is determined by the electronic excitations produced in the ice, rather than by knock-on collisions (Brown et al., 1978) and, hence, is an electronically-stimulated-desorption process. This exciting discovery opened a new field of study. Below the relevance of desorption to a few outer solar system bodies is described; for extended descriptions see Johnson (1990; 1996; 1998).II Desorption from Solar System BodiesThe samples collected during the Apollo missions show the lunar surface is modified by the impacting solar-wind ions (~ 1 keV/u H+ and He++) and by energetic solar particles (Taylor, 1982). This aspect of planetary physics has recently been revived by the observation of Na and K 'atmospheres' around Mercury and the Moon (Potter and Morgan, 1985; 1988). Such atmospheres are produced by stimulated-desorption (the ions, electrons and UV photons) of these atoms from the rocky surfaces (Madey et al. 1998). The sodium atmosphere has been seen to extend to ~ 5 lunar radii from the moon's surface (Flynn and Mendillo, 1993), providing an impressive manifestation of desorption.

Saturn’s moon Enceladus emits plumes of water vapour and ice particles from fractures near its south pole1–5, suggesting the possibility of a subsurface ocean5–7. These plume particles are the dominant source of Saturn’s E ring7,8. A previous in situ analysis9 of these particles concluded that the minor organic or siliceous components, identified in many ice grains, could be evidence for interaction between Enceladus’ rocky core and liquid water9,10. It was not clear, however, whether the liquid is still present today or whether it has frozen. Here we report the identificationof a population of E-ring grains that are rich in sodium salts ( 0.5–2% by mass), which can arise only if the plumes originate from liquid water. The abundance of various salt components in these particles, as well as the inferred basic pH, exhibit a compelling similarity to the predicted composition of a subsurface Enceladus ocean in contact with its rock core11. The plume vapour is expected to be free of atomic sodium. Thus, the absence of sodium from optical spectra12 is in good agreement with our results. In the E ring the upper limit for spectroscopy12 is insufficientlysensitive to detect the concentrations we found.

Growls from the Tiger Stripes: the Latest on EnceladusJennifer G. Winters

4. Tiger StripesAs stated above, the ’tiger stripes’ were the first indication of interesting activity inthe south pole. These are four roughly parallel fractures, each about 130 km long and 300m deep, flanked by ridges 100 m high. As the radius of Endeladus is only 250 km,the fact that these features are so sizeable is remarkable. It is thought that these featureswere formed by the upwelling of low density material (diapirism) as a result of tidal heating(Nimmo & Pappalardo 2006). Figure 1 (from Porco et al. 2006) shows these fractures atincreasing magnifications in composites from Cassini’s NAC (Narrow Angle Camera). Thefalse blue-green color of B and C indicates the relatively coarse-grained ice particles that liewithin and just along the tiger stripes.The temperature in the area of the tiger stripes is much higher than that of the surroundingareas (114-157 K vs. 74-81 K) (Porco et al. 2006), due to a still unknowngeothermal source (see H 4.1 for further discussion), but it has been determined that thehigh temperatures originate in or under the tiger stripes.4.1. Geothermal ActivityMany have puzzled over the source of the abnormally high thermal activity occurringat the tiger stripes. 4-8 GW of energy is being released from this area, known as the southpolar thermal anomaly. Radiogenic sources (those that release heat from radioactive decayin an assumed differentiated chondritic rocky core) can only contribute 0.32 GW of this heat.Other suggestions include shear heating from tidal forces (Nimmo & Pappalardo et al. 2007;Hurford et al. 2007) and influences from the near-resonance with Dione (another of Saturn’smoons) (Squyres et al. 1983). While these appear to be the most widely accepted causesfor the high energy being observed, Tobie et al. (2008) have proposed that friction due tolow viscosity in the boundary between the overlying ice layer and a possible subsurface seacould generate enough energy to explain this thermal activity.Abramov & Spencer (2009) observe that over the 16 month period between Cassiniflybys, the thermal emission varied by less than 15%, so it seems to be staying fairly constantat this time. But Tobie et al.(2008) note that if there is liquid at depth, it is impossible tosustain it over long timescales if the heat output is this great. Based on this, they proposethat the thermal emission rate at this time is abnormally high. And as if it is not difficultenough to explain the extra heat, they have pointed out that this 4-8 GW of observedenergy does not include radiation that is outside the wavelength detection limits of theCIRS (Composite Infrared Spectrometer) (7-1000 μm) or any heat flow from regions otherthan the south polar area, so the total energy is probably even more than that observed.This issue will remain a mystery until more conclusive data is received.The location of this south pole anomaly (SPT) is also perplexing. Why are there tigerstripes only at the south pole and not at both poles? Tobie et al. (2008) and Collins &Goodman (2007) suggest that a negative gravity anomaly created by a subsurface sea, whichis created by the thermal output, will tend to reorient the satellite’s rotation axis so that thehotspot is always at the south pole. This idea is a modification of one proposed by Nimmo& Pappalardo (2006).Figure 2 (from Tobie et al. 2008) shows a schematic of their model of the geothermalprocesses occurring at the south pole, including a silicate core, a layer of liquid water, alayer of warm ice, and then the overlying cold ice surface. Also illustrated are the vents andplumes and the ’negative gravity anomaly’ due to the accumulation of melt.

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

Interesting overview of reasons of certain hypotheses pertaining to outgassing from oceans on Enceladus, fun and a bit saddening to read as there seems to be something overlooked along the way. It stands in sharp contrast with the ideas in the in the text following this one.

4.2 Eruption Processes, Plume-Surface Interactions and DepositsIo, Enceladus and Triton are the only bodies on which eruptions have been observed.Plumes on Io, Enceladus, and Triton provide insights into their sub-surface volatiles andprocesses. These plume activities are responsible for the generation of transient and tenuousatmospheres around these moons and for deposits that give Io and Triton their distinctiveappearance, and subtly affect features on Enceladus. Europa and Titan are two other moonson which eruptive processes are likely to have occurred in the very recent past, but direct evidenceis still lacking. The presence of methane and argon on Titan suggests that outgassingand hence eruptions have occurred during much of its history. On Europa, several surfacefeatures suggest that effusive processes have recently occurred.4.2.2 EnceladusThe Enceladus plume emerges from discrete sources (Spitale and Porco 2007) located on asystem of cracks in the ice crust (Spencer et al. 2006). Although a certain variability of theplume activity is expected from the response of the cracks to tidal stresses (Hurford et al.2007), the plume appears surprisingly steady over the time it has been observed. Similargas densities are derived from stellar plume occultations recorded by the Cassini UltravioletImaging Spectrograph (UVIS) with an increase by a factor of 1.7 from 2005 (Hansen et al.2006) (1.5 × 1016 molecules per cm2 for a line of sight passing at 15 km altitude overthe south pole) to 2007 (Hansen et al. 2008). Moreover, unchanged individual dust jets areobserved in images taken over more than two years (Spitale and Porco 2007), which furthersupports the idea that the plume sources remain active over long periods.Such a continuous plume activity requires a steady mechanism for the production ofgas and grains. Explosive and self-limiting processes appear implausible (Brilliantov et al.2008). This excludes geyser-like processes, with a build up of pressure, suddenly releasedin an eruption, and it rules out the so-called cold faithful model (Porco et al. 2006). Also thedecomposition of clathrates (Kieffer et al. 2006) seems difficult to reconcile with the steadyproduction of gas and grains, although this idea is attractive since it offers an explanationfor the observed abundance of roughly 10% of volatile gases (CO2, N2, CO) in the plumegas (Waite et al. 2006).Alternative scenarios for the production of gas are direct evaporation either from liquidwater (Schmidt et al. 2008; Postberg et al. 2009) or warm ice (Nimmo et al. 2007) at depthunder the ice crust. In these models the gas flows through cracks in the ice to surface. At thesite of evaporation the gas is in near thermal equilibrium with the water and/or ice. When thevapour is accelerated it expands and cools, in accordance with the laws of thermodynamics,and thus becomes super-saturated, and ice grains may condense from the vapour.When a new crack is opened in the ice crust both models (sublimation from liquid orwarm ice) lead to a nearly steady state after a transition period, in which the gas slowlyheats the ice in the vicinity of the crack. Initially, the vapour will condense entirely at depthon the cold crack walls and by latent heat of condensation the ice will gradually warmup. Eventually, the process approaches a steady state when the heat flow in the ice is inequilibrium with the radiative loss at the surface and the heat supplied by advection bythe gas from depth. This transition to the steady state may take hundreds of years for acrack of several kilometers depth (Ingersoll and Pankine 2010). During this period narrowcracks might even be sealed by the condensing vapour before the gas flow reaches vacuum.Systems of nearby cracks may act together heating the ice in their vicinity. In steady statecondensation at the walls will be mostly limited to the region close to the surface, sincethere the temperature gradient, and thus the heat flow, is largest. In this way a conduit shouldnaturally develop its narrowest point near the surface.Averaging over more complex channel profiles, Schmidt et al. (2008) obtained a differentialparticle size distribution for the condensed grains which has a slope correspondingto an exponent of −4 for grains in the size range of one micron but globally falling offsteeper than a power law. Also, the distribution exhibits a local minimum for submicronsized grains. This distribution is consistent with the narrow E ring size distribution derivedfrom pre Cassini data (Showalter 1991; Nicholson et al. 1996) and Cassini CDA data (Kempfet al. 2008).From the structure of the dust plume seen in images it was early concluded that most ofthe grains must fall back to the surface, ejected at a mean speed of 120 m/s (Porco et al.2006), which is smaller than Enceladus’ escape speed of 240 m/s. The plume model ofSchmidt et al. (2008) gives a mean grain speed of 100 m/s, which is practically the samenumber. The velocity distribution was recently constrained (Hedman et al. 2009) from a detailedanalysis and modeling of spectral slopes of the plume obtained from data taken bythe Cassini Visual and Infrared Mapping Spectrometer (VIMS). The authors find clear evidencethat large particles (around 3 micron radius) are ejected at low velocities, practicallyall falling back to the surface and populating the lower parts of the plume, while smallerparticles are systematically faster.Altogether, the low speed of the ejected grains appears surprising, since large gas speedson the order of 500 m/s were inferred from Cassini UVIS data (Hansen et al. 2006;Tian et al. 2007). If grains condense in the gas, one would expect them to have the samevelocity. If the grains are formed by some other mechanism, then the gas must be sufficientlydense to accelerate them. Also in this case the grain will rapidly reach gas speed,again in contradiction to the observations.There are in principle two ways to understand the slow velocity of the dust compared tothe gas. One possibility (Schmidt et al. 2008) is that frequent collisions of grains with thevent walls repeatedly decelerate the grains relative to the gas. Such collisions are in practiceunavoidable in a realistic channel, i.e. one that is not perfectly straight, since the streamlinesof the gas and the trajectories will differ. Owing to their smaller speeds, large grains populatethe plume at lower altitudes. This model reproduces the particle densities measured by CDA(Schmidt et al. 2008), the brightness of the plume seen in images, and the gas production rateinferred by INMS and UVIS. Another possibility to obtain in principle slow grains and fastgas is that the gas and dust decouple only in the uppermost, funnel shaped, part of a channel.In this region the gas is further accelerated by the pressure drop from the channel to vacuum,while it simultaneously dilutes by large factors. If this mechanism works quantitatively,simulating the observed particle speed-size distribution (Hedman et al. 2009) remains to beverified.The composition of ejected material addresses the question of whether liquid water orwarm ice is Enceladus’ primary plume source (Zolotov 2007). If the jets originate fromsublimating ice, trapped gases would be the major non-water compound, whereas mineralsleached from the large Enceladian rock core should be present in a possible subsurfaceocean. In the latter case Na+ and Cl− ions, are expected to be the most abundant non-waterspecies, followed by bicarbonate (HCO−3 ) and K+ (Zolotov 2007). During the slow downwardfreezing expected after formation of icy planetary bodies, alkali salts always stay in theliquid phase and the ice crust remains practically salt free. On one hand the abundant detectionof CO2, CH4, N2 and/or CO in the plume vapour (Waite et al. 2006) suggest the presenceof clathrate hydrates and gave rise to the proposition that the decomposition of such ices isthe actual plume driver (Kieffer et al. 2006). On the other hand the in situ measurements ofCassini CDA show alkali metals in 93% of mass spectra from E ring ice grains (Postberget al. 2009). The E ring can be considered as a storage ring for previously ejected plumegrains. Whereas most of these grains show only traces of sodium and potassium (Na/H2O≈ 10−7), about 6% exhibit a salt content increased by several orders of magnitude (Na/H2O≈ 10−2–10−3). Particles with intermediate concentrations are rare (<3%).The Na-rich CDA spectra imply 0.05–0.2M/kg NaCl and 0.02–0.1M/kg NaHCO3 yieldingan alkaline pH of 8.5–9 in a liquid with the ice grains composition. This is in compellingsimilarity with the model calculations (Zolotov 2007). However, the inferred Na/K ratio of100–300 is about 10 times higher than expected from the solar abundance. The presenceof salts in concentration as found in Na-rich E ring grains is difficult to reconcile with icesublimation (Nimmo et al. 2007) or clathrate decomposition as the main plume producingprocess (Kieffer et al. 2006). The observed composition strongly favors an origin from waterthat is or has been in contact with the rocky core.The non-water molecules found in the plume vapour (Waite et al. 2006) suggest clathratedecomposition as a parallel process. Although probably not relevant as a plume driver, gasrelease from clathrates might take place at ice/water interfaces of the source or in ice layersabove such a reservoir. However, a “Soda Ocean” rich in bicarbonates could also work as asource of CO2. Hydrothermal processes (Matson et al. 2007) might also be considered forthe production of N2, CH4, and other organic compounds. Postberg et al. (2009) introducea scenario in which Na-rich and Na-poor grain populations are both produced from liquidplume sources (Fig. 8): Na-rich ice grains are formed by freezing of aerosols created by ascendinggas bubbles (e.g. from CO2) or other turbulent processes in the liquid. The Na-poorgrains (which represent the main E ring population) are suggested to stem from nucleationof the supersaturated vapour (Fig. 8B) as suggested by Schmidt et al. (2008). Trace amountsof NaCl molecules (present in low concentration in the liquid Zolotov 2007) can traversefrom liquid solution into the gas phase. Due to its high energy of solution, a significantNa escape via the plume gases is not expected and in agreement with the non detection byCassini instruments and Earth bound spectroscopy (Schneider et al. 2009). One might consider the possibility of parallel venting mechanisms from a liquid and fromwarm ice. The first would produce the Na-rich grains, the latter the majority of non-waterplume gases and Na-poor grains. However, the formation of Na-rich particles requires aliquid reservoir, so evaporation above such a liquid is probably the most plausible driver forEnceladus’ plumes in general.From heat flow arguments it can be shown that the liquid/gas interface below Enceladus’surface must be orders of magnitude larger than the vent cross sections, otherwise implausiblylarge temperature gradients would be necessary to balance the loss due to latent heat(Postberg et al. 2009). Therefore large vapour chambers which narrow to the vent channelsare required above a liquid plume source.

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

Unlike the previous text, this one is I think a recommended read. Gives a nice oversight of ideaswhich do deserve to be given more attention, as the authors ask for. There seems to be some light coming through the cracks in the fabric of dull science.

Space weathering is the collection of physical processes acting to erode and chemically modifyplanetary surfaces directly exposed to space environments of planetary magnetospheres, theheliosphere, and the local interstellar environment of the solar system. Space weathering affectsthe physical and optical properties of the surfaces of planetary bodies, so understanding itsspecifics is critical for interpreting surface data from remote and landed measurements. For fullcoverage of space environmental measurements, we recommend expanded interdisciplinarycooperation between NASA’s Planetary Science and Heliophysics divisions. To grow the fieldin the next decade and maximize impact on mission studies, we suggest a balanced mixture oflaboratory measurements, modeling, and theoretical investigations in support of all missions.

Space Environments

Vast expanse of the space weathering environment interacting with solar system bodies isillustrated in Figure 1 by logarithmic horizontal scale of radial distance from the Sun to α-Centauri. Principal sources of energy for space weathering of planetary surfaces are UV photons,solar wind plasma, and energetic particles from the Sun, within a few hundred AU, and externalsources of plasma and energetic particles entering into the solar system from the local interstellarenvironment. Beyond the realm of terrestrial planets and the asteroid belts, the solar influencesignificantly wanes with the decline in density of the expanding solar wind plasma andmagnitude of the frozen-in magnetic field, while the interstellar influence progressively growsthrough interaction of interstellar neutral winds with solar ultraviolet radiation and the solar windplasma. Across the heliospheric boundary region near 100 AU, now being explored by the twoVoyager spacecraft, occurs a transition from supersonic (400 – 800 km/s) plasma flows of solarcoronal expansion, the solar wind, to 26 km/s inward flow of the interstellar wind. This plasmacontains both a bulk flow and thermal components associated with typical ion energies up to afew keV, and energetic components extending to far higher energies, ultimately to the full rangeof galactic cosmic ray ions easily penetrating into the heliosphere at GeV energies and higher.The Sun contributes the innermost source of energetic particles in association with solar flareand coronal mass ejection (CME) events, the interstellar environment contributes the outermostsources, and the dynamics of the expanding and variable solar wind provide additional energy toMeV energies within the heliosphere. The solar wind termination shock, the supersonic-subsonicflow boundary crossed by both Voyagers (Stone et al., 2005, 2008), and/or the heliosheath regionbeyond this shock out to the heliopause, the contact boundary with interstellar plasma, mayfurther accelerate plasma particles into the energetic range but this is not yet established by theVoyager measurements. Neither spacecraft detected local particle acceleration at the respectivecrossings, although the bulk of acceleration may be occurring elsewhere along the shockboundary (McComas and Schwadron, 2006). Other possibilities are that the heliosheath ions areenergized by turbulent or reconnecting magnetic fields in the heliosheath, or that these ionsoriginate instead from penetrating interstellar ions (Cooper et al., 2006; Cooper, 2008). As solaractivity increases and then again declines within the next decade from the current minimum, thecontinuing Voyager measurements, supplemented by direct energetic neutral atom measurementsof boundary region emissions by the Interstellar Boundary Explorer (IBEX) in earth orbit, areexpected to resolve origin of the heliosheath ions and to locate the heliopause. What is alreadyclear is that the termination shock boundary marks the transition from dominance of some spaceweathering effects, e.g. erosive sputtering, by the supersonic plasma flow to a broader range ofeffects from plasma and energetic particles at higher energies to the cosmic ray regime.Within these expanding near-solar to heliospheric to local interstellar space environments wefind the objects of primary interest to planetary science: the terrestrial planets, the asteroid belt,the gas and ice giant planets, comets, the Kuiper Belt, and finally the Oort Cloud. Aside from thefirst known member of the Kuiper Belt, Pluto, now officially designated as an ice dwarf planet,our direct knowledge of Kuiper Belt Objects (KBO) began with the first discovery in 1992, thenfollowed to date by about a thousand other discoveries of such objects, including a few classifiedas members of the inner Oort Cloud. Presumably there are thousands more of similarlydetectable size waiting to be discovered, and far more at smaller sizes. Looking back towards theSun, there are also thousands of known asteroidal bodies, including Near Earth Objectspotentially of concern for future Earth impacts, and as a remote possibility the first members ofthe fabled Vulcanoid Belt that might be found via increasing sensitivity of near-solarobservations. At the smallest scales there are interplanetary dust grains, the source of thezodiacal light, extending down in size to nanometers or less (e.g., molecular clusters) andthought to arise from impact surface weathering of small bodies and from comet outgassing.The red and white stars of Figure 1 denote the distinctly different space environments of solarsystem bodies with and without internally generated magnetic fields. Except for the highestenergy cosmic rays and their atmospheric interaction products, the direct effects of spaceweathering do not extend to the solid surfaces of Venus, Earth, and Mars. While the planetarymagnetospheres (red stars) substantially deflect interplanetary plasmas and energetic particlesaway from the atmospheres and underlying surfaces, even an ionospheric (white star) interactionarising from ionization of a thin atmosphere, or surface-bound exosphere, can significantlyimpede or totally inhibit access of space plasma to otherwise exposed surfaces. The surface ofMars is notably oxidized by solar ultraviolet irradiation and to a lesser extent from high energy(> 100 MeV) cosmic rays and solar energetic particles, while medium-energy (> 1 MeV)energetic ions can easily penetrate Pluto’s microbar-pressure atmosphere to the surface. On theother hand, the acceleration of charged particles within the planetary magnetospheres, andmagnetic pickup of exospheric ions, provides additional and potentially more dominant energysources for space weathering of surfaces exposed to those environments.

Support comprehensive specification of space weathering environments through expansion ofcooperation between NASA heliophysics and planetary science divisions on placement ofenvironmental radiation instrumentation on appropriate missions, compilation of data andsemiempirical models from measurements, and on predictive models for each environment.Rationale: In the heliophysics community there is the concept of the Heliophysics Global Observatory(HGO), the collective fleet of operational heliophysics missions, that should be expanded forinterdisciplinary applications to include planetary missions. Heliophysics support for space environmentmodeling, e.g. the Earth-Moon-Mars Radiation Environment Module (Schwadron et al., 2007) and earlier(e.g., NASA GSFC, JPL) models for solar and cosmic ray energetic particle modeling in the terrestrialplanet domain, can be usefully applied to planetary interaction applications. Similarly, missions and datamodels for planetary interactions can also support investigation and modeling of interplanetaryenvironments. HGO data virtual observatory approaches could be applied to planetary missions.

Encourage community-wide and interdisciplinary investigations of universal space weatheringprocesses through balanced mixture of initiatives on mission instrument data analysis,laboratory measurements, computational modeling, and relevant theoretical investigations.Rationale: The space environment is universal in the sense of connecting all the planetary environments,and so it most efficient to approach space weathering processes from the universal perspective, e.g. thatsimilar processes act everywhere and the effects differ only in the relative energy deposition rates andcompositional impacts of each process in different locations. Process investigations must be wellgroundedin measurements for different environments, in broad-spectrum approaches to laboratorysimulations, and best available inputs from theory and high performance computing.

Enable development of plasma ion, energetic particle, and neutral composition spectrometersfor in-situ analyses to characterize elemental and isotopic range of interconnected planetarysurface, atmospheric, ionosopheric, magnetospheric, and heliospheric environments.Rationale: Our knowledge of composition in these environments beyond the Earth is limited to somemajor species with little or no information on the full range of elemental and isotopic composition that iscritical to determination of origins, evolutionary processes, and astrobiological potential. Sample return istoo expensive for general application, advanced in-situ analysis capabilities being required for one-waymissions to most non-terrestrial destinations of the solar system. There is also strong coupling ofcomposition for these connected environments and this coupling should be considered in weighting therelative priorities of measurements in each environment.

Provide facilities for more realistic laboratory science and engineering simulations ofplanetary surface environments under simultaneous influence of extreme limits on pressure,temperature, radiation, composition, physical structure, and endogenic or impact activity.Rationale: There are no truly flat surfaces, particularly when viewed at the microscopic level of mostspace weathering processes, and multiple energy sources are typically operating on affected surfaces. Thesensible and accessible surfaces have impact regolith layers extending to meters in depth and likely withhigh porosity under conditions of reduced gravity. Multi-phase interactions of ice, grains, and volatiles inirradiated bulk surface samples need much further investigation with appropriate facilities. Engineeringsimulation facilities require development to support realistic and extreme environment testing for futureorbital and landed missions to irradiated icy bodies such as at Europa, Ganymede, Enceladus, and Triton

The illusion from which we are seeking to extricate ourselves is not that constituted by the realm of space and time, but that which comes from failing to know that realm from the standpoint of a higher vision. -L.H.

Don't forget the April 20th announcement from the Cassini team that they had discovered and measured a very strong electric current (aka "flux tube with an axial electron beam") that is correlated with a co-revolving northern auroral footprint, seen in UV light. They did not write up their estimate for the current strength (amperage), but the very similar one found connecting Io with Jupiter's northern and southern auroral ovals was estimated at 2 trillion amps. The team also did not mention that there might be southern hot spot on Saturn similar to Jupiter's, nor that if found it may represent the return side of the electric circuit circulating through Enceladus's polar regions.

In particular, the "anomalous" or "tidal" heating in the tiger stripes area centered around Enceladus's south pole, where geysers (ion and electron mass ejections) are observed, may simply be local Joule or ohmic heating of the crustal material there where the current flows into the moon. It is not simply local heating that is ejection or "mass loading" Enceladus's ionosphere and plasma torus with electrons,water ions and ionized salt molecules at the rate of approximately 100 kg/s. c.o.n.n.e.c.t the dots!

Last year, scientists predicted that some of the material spewed out into space by the icy geysers at Enceladus's south pole would slowly fall down to certain areas on the surface. Detailed measurements by NASA's planetary probe Cassini, presented at the meeting, have now revealed the predicted snow fields, which measure up to 100 meters thick. They betray their presence by their conspicuous bluish color and by softening the outlines of buried craters and canyons (inset).

"More than 90 jets of all sizes near Enceladus's south pole are spraying water vapor, icy particles, and organic compounds all over the place," says Carolyn Porco, an award-winning planetary scientist and leader of the Imaging Science team for NASA's Cassini spacecraft. "Cassini has flown several times now through this spray and has tasted it. And we have found that aside from water and organic material, there is salt in the icy particles. The salinity is the same as that of Earth's oceans."

In a new study, Hill and colleagues describe what they found in the data from Cassini: a new class of space particles — submicroscopic "nanograins" of electrically charged dust. Such particles are believed to exist throughout the universe, and this marks the first time researchers have measured and analyzed them.

"The nanograins are in a 'Goldilocks' size regime that no one's seen before: not too big and not too small to influence, and be influenced by, the plasma," Hill said. "That's one of the things that makes them interesting."For instance, because of their size, nanograins are noticeably affected by both gravitational and electromagnetic forces. This contrasts sharply with both larger particles that are dominated by gravity and smaller charged particles that are dominated by electromagnetic forces.

... because they lie in a theoretically important but previously unobserved range where particles have an intermediate mass-to-charge ratio,"

There have been three Cassini encounters with the south-pole eruptive plume of Enceladus for which the Cassini Plasma Spectrometer (CAPS) had viewing in the spacecraft ram direction. In each case, CAPS detected a cold dense population of heavy charged particles having mass-to-charge (m/q) ratios up to the maximum detectable by CAPS (∼104 amu/e). These particles are interpreted as singly charged nanometer-sized water-ice grains. Although they are detected with both negative and positive net charges, the former greatly outnumber the latter, at least in the m/q range accessible to CAPS. On the most distant available encounter (E3, March 2008) we derive a net (negative) charge density of up to ∼2600 e/cm3 for nanograins, far exceeding the ambient plasma number density, but less than the net (positive) charge density inferred from the RPWS Langmuir probe data during the same plume encounter. Comparison of the CAPS data from the three available encounters is consistent with the idea that the nanograins leave the surface vents largely uncharged, but become increasingly negatively charged by plasma electron impact as they move farther from the satellite. These nanograins provide a potentially potent source of magnetospheric plasma and E-ring material.

The nature of the Enceladus plume has been revealed over time due to the synergistic nature of the fields and particles instruments on Cassini, which has been in residence in Saturn's magnetosphere since 2004. Following the original detection of the plume based on magnetometer measurements, Sven Simon from the University of Cologne, Germany, and Hendrik Kriegel from the University of Braunschweig, Germany, found that the observed perturbation of Saturn's magnetic field required the presence of negatively charged dust grains in the plume. These findings were reported in the April and October 2011 issues of Journal of Geophysical Research Space Physics. Previous data obtained by the ion and neutral mass spectrometer revealed the complex composition of the plume gas, and the cosmic dust analyzer revealed that the plume grains were rich in sodium salts. Because this scenario can only arise if the plume originated from liquid water, it provides compelling evidence for a subsurface ocean.

* Enceladus' diameter is about 500 km, so it probably has no liquid water now, just frozen. But electrical forces that produce the geysers may melt the ice briefly before shooting the vapors into space. Ted said the salinity is the same as that of Earth's oceans. That may be good support for Cardona's and others' theory that Earth was a moon of Saturn a few thousand years ago.

You're free to comment as you wish but if you want to spread the word about EU I'd suggest using a less antagonistic tone. There must be thousands of genuinely enquiring minds out there who would gladly look at a useful link or consider a well stated idea. I know insulting people is de rigeur on Youtube but it doesn't actually help win them over.

tayga

It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong.- Richard P. Feynman

Normal science does not aim at novelties of fact or theory and, when successful, finds none.- Thomas Kuhn